[Blazor] Ensure System.Text.Json RespectRequiredConstructorParametersDefault can be enabled (#62366)

* Enable `RespectRequiredConstructorParametersDefault` to ensure it can be set on user's apps.
* Add a null parameter default value to the ResourceAsset constructor.

Author: Copilot

src/Components/Components/src/PublicAPI.Shipped.txt

@@ -417,7 +417,6 @@ Microsoft.AspNetCore.Components.RenderTree.RenderTreeFrameType.Region = 5 -> Mic
 Microsoft.AspNetCore.Components.RenderTree.RenderTreeFrameType.Text = 2 -> Microsoft.AspNetCore.Components.RenderTree.RenderTreeFrameType
 Microsoft.AspNetCore.Components.ResourceAsset
 Microsoft.AspNetCore.Components.ResourceAsset.Properties.get -> System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Components.ResourceAssetProperty!>?
-Microsoft.AspNetCore.Components.ResourceAsset.ResourceAsset(string! url, System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Components.ResourceAssetProperty!>? properties) -> void
 Microsoft.AspNetCore.Components.ResourceAsset.Url.get -> string!
 Microsoft.AspNetCore.Components.ResourceAssetCollection
 Microsoft.AspNetCore.Components.ResourceAssetCollection.IsContentSpecificUrl(string! path) -> bool

src/Components/Components/src/PublicAPI.Unshipped.txt

@@ -1,4 +1,5 @@
 #nullable enable
+Microsoft.AspNetCore.Components.ResourceAsset.ResourceAsset(string! url, System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Components.ResourceAssetProperty!>? properties = null) -> void
 Microsoft.AspNetCore.Components.Routing.Router.NotFoundPage.get -> System.Type!
 Microsoft.AspNetCore.Components.Routing.Router.NotFoundPage.set -> void
 Microsoft.AspNetCore.Components.Infrastructure.ComponentsMetricsServiceCollectionExtensions

src/Components/Components/src/ResourceAsset.cs

@@ -12,7 +12,7 @@ namespace Microsoft.AspNetCore.Components;
 /// <param name="url">The URL of the resource.</param>
 /// <param name="properties">The properties associated to this resource.</param>
 [DebuggerDisplay($"{{{nameof(GetDebuggerDisplay)}(),nq}}")]
-public sealed class ResourceAsset(string url, IReadOnlyList<ResourceAssetProperty>? properties)
+public sealed class ResourceAsset(string url, IReadOnlyList<ResourceAssetProperty>? properties = null)
 {
     /// <summary>
     /// Gets the URL that identifies this resource.

src/Components/Components/test/ResourceAssetCollectionTest.cs

@@ -1,6 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
 namespace Microsoft.AspNetCore.Components;
 
 public class ResourceAssetCollectionTest
@@ -85,4 +88,68 @@ [new ResourceAssetProperty("label", "image2.jpg")]),
         Assert.False(isContentSpecificUrl1);
         Assert.True(isContentSpecificUrl2);
     }
+
+    [Fact]
+    public void ResourceAsset_CanSerializeAndDeserialize_WithoutRespectRequiredConstructorParameters()
+    {
+        // Arrange
+        var originalAsset = new ResourceAsset("test-url", null);
+        var options = new JsonSerializerOptions { WriteIndented = true };
+
+        // Act
+        var json = JsonSerializer.Serialize(originalAsset, options);
+        var deserializedAsset = JsonSerializer.Deserialize<ResourceAsset>(json, options);
+
+        // Assert
+        Assert.NotNull(deserializedAsset);
+        Assert.Equal("test-url", deserializedAsset.Url);
+        Assert.Null(deserializedAsset.Properties);
+    }
+
+    [Fact]
+    public void ResourceAsset_CanSerializeAndDeserialize_WithRespectRequiredConstructorParameters()
+    {
+        // Arrange
+        var originalAsset = new ResourceAsset("test-url", null);
+        var options = new JsonSerializerOptions 
+        { 
+            WriteIndented = true,
+            RespectRequiredConstructorParameters = true
+        };
+
+        // Act
+        var json = JsonSerializer.Serialize(originalAsset, options);
+        var deserializedAsset = JsonSerializer.Deserialize<ResourceAsset>(json, options);
+
+        // Assert
+        Assert.NotNull(deserializedAsset);
+        Assert.Equal("test-url", deserializedAsset.Url);
+        Assert.Null(deserializedAsset.Properties);
+    }
+
+    [Fact] 
+    public void ResourceAsset_WithSourceGenerationContext_CanSerializeAndDeserializeWithRespectRequiredConstructorParameters()
+    {
+        // Arrange - this test simulates the context from ResourceCollectionUrlEndpoint
+        var originalAsset = new ResourceAsset("test-url", null);
+        var assets = new List<ResourceAsset> { originalAsset };
+        
+        // Use a custom JsonSerializerOptions that mimics the source-generated context behavior
+        var options = new JsonSerializerOptions
+        {
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault,
+            WriteIndented = false,
+            RespectRequiredConstructorParameters = true
+        };
+
+        // Act
+        var json = JsonSerializer.Serialize<IReadOnlyList<ResourceAsset>>(assets, options);
+        var deserializedAssets = JsonSerializer.Deserialize<IReadOnlyList<ResourceAsset>>(json, options);
+
+        // Assert
+        Assert.NotNull(deserializedAssets);
+        Assert.Single(deserializedAssets);
+        Assert.Equal("test-url", deserializedAssets[0].Url);
+        Assert.Null(deserializedAssets[0].Properties);
+    }
 }

src/Components/test/testassets/Directory.Build.props

@@ -25,4 +25,9 @@
   <PropertyGroup>
     <BlazorCacheBootResources>false</BlazorCacheBootResources>
   </PropertyGroup>
+  
+  <ItemGroup>
+    <!-- Enable RespectRequiredConstructorParametersDefault to test compatibility -->
+    <RuntimeHostConfigurationOption Include="System.Text.Json.Serialization.RespectRequiredConstructorParametersDefault" Value="true" />
+  </ItemGroup>
 </Project>